Field of the Invention
The present disclosure relates to a positive electrode active material for a non-aqueous secondary battery, such as a lithium-ion secondary battery.
Description of the Related Art
In recent years, mobile electric devices, such as a VTR, a cell phone, and a laptop personal computer, have spread and are miniaturized, and, as a power source for such mobile devices, non-aqueous secondary batteries, such as lithium-ion secondary batteries, are being used. Further, recently, environmental problems must be dealt with and therefore, the non-aqueous secondary batteries are attracting attention as a power battery for, e.g., an electric vehicle.
As an example of a positive electrode active material for the lithium-ion secondary battery, a lithium-cobalt composite oxide having a layer structure has been practically used. However, the lithium-cobalt composite oxide uses cobalt which is a rare resource, and hence is disadvantageous from the viewpoint of the cost. In view of this, a lithium-nickel composite oxide having a layer structure using nickel instead of cobalt is studied. The lithium-nickel composite oxide has a large charge-discharge capacity per unit mass, as compared to the lithium-cobalt composite oxide; however, the lithium-nickel composite oxide has a problem in that, for example, synthesis of this oxide is difficult. Therefore, the lithium-nickel composite oxide having part of the nickel replaced by another metal element is frequently used.
Meanwhile, there is a technique for treating the surface of lithium metal composite oxide particles with a coupling agent.
For the purpose of suppressing the deterioration of cycle characteristics and others due to moisture adsorption, JP 2000-281354A discloses a technique for treating the surface of lithium metal composite oxide particles, such as Li1.03Ni0.8 Co0.2O2, with a coupling agent, such as isopropyltriisostearoyl titanate.
On the other hand, there is also a technique for washing a lithium metal composite oxide, such as a lithium-nickel composite oxide, according to the purpose.
For the purpose of suppressing a lowering of the high rate discharge capacity of a non-aqueous battery using LiNiO2 as a positive electrode active material, JP H06-111820A discloses the reduction of the content of lithium-containing water-soluble impurities in the positive electrode active material to a predetermined content or lower, and a technique for washing with water or an acid the LiNiO2 having such a reduced impurity content which is obtained through heating treatment.